#!/bin/sh
#
# Copyright (c) 2007 Andy Parkins
#
# An example hook script to mail out commit update information.  This hook
# sends emails listing new revisions to the repository introduced by the
# change being reported.  The rule is that (for branch updates) each commit
# will appear on one email and one email only.
#
# This hook is stored in the contrib/hooks directory.  Your distribution
# will have put this somewhere standard.  You should make this script
# executable then link to it in the repository you would like to use it in.
# For example, on debian the hook is stored in
# /usr/share/doc/git-core/contrib/hooks/post-receive-email:
#
#  chmod a+x post-receive-email
#  cd /path/to/your/repository.git
#  ln -sf /usr/share/doc/git-core/contrib/hooks/post-receive-email hooks/post-receive
#
# This hook script assumes it is enabled on the central repository of a
# project, with all users pushing only to it and not between each other.  It
# will still work if you don't operate in that style, but it would become
# possible for the email to be from someone other than the person doing the
# push.
#
# Config
# ------
# hooks.mailinglist
#   This is the list that all pushes will go to; leave it blank to not send
#   emails for every ref update.
# hooks.announcelist
#   This is the list that all pushes of annotated tags will go to.  Leave it
#   blank to default to the mailinglist field.  The announce emails lists
#   the short log summary of the changes since the last annotated tag.
# hooks.envelopesender
#   If set then the -f option is passed to sendmail to allow the envelope
#   sender address to be set
# hooks.emailprefix
#   All emails have their subjects prefixed with this prefix, or "[SCM]"
#   if emailprefix is unset, to aid filtering
# hooks.showrev
#   The shell command used to format each revision in the email, with
#   "%s" replaced with the commit id.  Defaults to "git rev-list -1
#   --pretty %s", displaying the commit id, author, date and log
#   message.  To list full patches separated by a blank line, you
#   could set this to "git show -C %s; echo".
#
# Notes
# -----
# All emails include the headers "X-Git-Refname", "X-Git-Oldrev",
# "X-Git-Newrev", and "X-Git-Reftype" to enable fine tuned filtering and
# give information for debugging.
#

# ---------------------------- Functions

#
# Top level email generation function.  This decides what type of update
# this is and calls the appropriate body-generation routine after outputting
# the common header
#
# Note this function doesn't actually generate any email output, that is
# taken care of by the functions it calls:
#  - generate_email_header
#  - generate_create_XXXX_email
#  - generate_update_XXXX_email
#  - generate_delete_XXXX_email
#  - generate_email_footer
#
 generate_email()
 {
         # --- Arguments
         oldrev=$(git rev-parse $1)
         newrev=$(git rev-parse $2)
         refname="$3"

         # --- Interpret
         # 0000->1234 (create)
         # 1234->2345 (update)
         # 2345->0000 (delete)
         if expr "$oldrev" : '0*$' >/dev/null
         then
                 change_type="create"
         else
                 if expr "$newrev" : '0*$' >/dev/null
                 then
                         change_type="delete"
                 else
                         change_type="update"
                 fi
         fi

         # --- Get the revision types
         newrev_type=$(git cat-file -t $newrev 2> /dev/null)
         oldrev_type=$(git cat-file -t "$oldrev" 2> /dev/null)
         case "$change_type" in
         create|update)
                 rev="$newrev"
                 rev_type="$newrev_type"
                 ;;
         delete)
                 rev="$oldrev"
                 rev_type="$oldrev_type"
                 ;;
         esac

         # The revision type tells us what type the commit is, combined with
         # the location of the ref we can decide between
         #  - working branch
         #  - tracking branch
         #  - unannoted tag
         #  - annotated tag
         case "$refname","$rev_type" in
                 refs/tags/*,commit)
                         # un-annotated tag
                         refname_type="tag"
                         short_refname=${refname##refs/tags/}
                         ;;
                 refs/tags/*,tag)
                         # annotated tag
                         refname_type="annotated tag"
                         short_refname=${refname##refs/tags/}
                         # change recipients
                         if [ -n "$announcerecipients" ]; then
                                 recipients="$announcerecipients"
                         fi
                         ;;
                 refs/heads/*,commit)
                         # branch
                         refname_type="branch"
                         short_refname=${refname##refs/heads/}
                         ;;
                 refs/remotes/*,commit)
                         # tracking branch
                         refname_type="tracking branch"
                         short_refname=${refname##refs/remotes/}
                         echo >&2 "*** Push-update of tracking branch, $refname"
                         echo >&2 "***  - no email generated."
                         exit 0
                         ;;
                 *)
                         # Anything else (is there anything else?)
                         echo >&2 "*** Unknown type of update to $refname ($rev_type)"
                         echo >&2 "***  - no email generated"
                         exit 1
                         ;;
         esac

         # Check if we've got anyone to send to
         if [ -z "$recipients" ]; then
                 case "$refname_type" in
                         "annotated tag")
                                 config_name="hooks.announcelist"
                                 ;;
                         *)
                                 config_name="hooks.mailinglist"
                                 ;;
                esac
                 echo >&2 "*** $config_name is not set so no email will be sent"
                 echo >&2 "*** for $refname update $oldrev->$newrev"
                 exit 0
         fi

         # Email parameters
         # The email subject will contain the best description of the ref
         # that we can build from the parameters
         describe=$(git describe $rev 2>/dev/null)
         if [ -z "$describe" ]; then
                 describe=$rev
         fi

         generate_email_header

         # Call the correct body generation function
         fn_name=general
         case "$refname_type" in
         "tracking branch"|branch)
                 fn_name=branch
                 ;;
         "annotated tag")
                 fn_name=atag
                 ;;
         esac
         generate_${change_type}_${fn_name}_email

         generate_email_footer
 }

 generate_email_header()
 {
         # --- Email (all stdout will be the email)
         # Generate header
         cat <<-EOF
         To: $recipients
         Subject: ${emailprefix}$projectdesc $refname_type, $short_refname, ${change_type}d. $describe
         X-Git-Refname: $refname
         X-Git-Reftype: $refname_type
         X-Git-Oldrev: $oldrev
         X-Git-Newrev: $newrev

         This is an automated email from the git hooks/post-receive script. It was
         generated because a ref change was pushed to the repository containing
         the project "$projectdesc".

         The $refname_type, $short_refname has been ${change_type}d
         EOF
 }

 generate_email_footer()
 {
         SPACE=" "
         cat <<-EOF


         hooks/post-receive
         --${SPACE}
         $projectdesc
         EOF
 }

# --------------- Branches

#
# Called for the creation of a branch
#
generate_create_branch_email()
{
         # This is a new branch and so oldrev is not valid
         echo "        at  $newrev ($newrev_type)"
         echo ""

         echo $LOGBEGIN
         show_new_revisions
         echo $LOGEND
}

#
# Called for the change of a pre-existing branch
#
generate_update_branch_email()
{
         # Consider this:
         #   1 --- 2 --- O --- X --- 3 --- 4 --- N
         #
         # O is $oldrev for $refname
         # N is $newrev for $refname
         # X is a revision pointed to by some other ref, for which we may
         #   assume that an email has already been generated.
         # In this case we want to issue an email containing only revisions
         # 3, 4, and N.  Given (almost) by
         #
         #  git rev-list N ^O --not --all
         #
         # The reason for the "almost", is that the "--not --all" will take
         # precedence over the "N", and effectively will translate to
         #
         #  git rev-list N ^O ^X ^N
         #
         # So, we need to build up the list more carefully.  git rev-parse
         # will generate a list of revs that may be fed into git rev-list.
         # We can get it to make the "--not --all" part and then filter out
         # the "^N" with:
         #
         #  git rev-parse --not --all | grep -v N
         #
         # Then, using the --stdin switch to git rev-list we have effectively
         # manufactured
         #
         #  git rev-list N ^O ^X
         #
         # This leaves a problem when someone else updates the repository
         # while this script is running.  Their new value of the ref we're
         # working on would be included in the "--not --all" output; and as
         # our $newrev would be an ancestor of that commit, it would exclude
         # all of our commits.  What we really want is to exclude the current
         # value of $refname from the --not list, rather than N itself.  So:
         #
         #  git rev-parse --not --all | grep -v $(git rev-parse $refname)
         #
         # Get's us to something pretty safe (apart from the small time
         # between refname being read, and git rev-parse running - for that,
         # I give up)
         #
         #
         # Next problem, consider this:
         #   * --- B --- * --- O ($oldrev)
         #          \
         #           * --- X --- * --- N ($newrev)
         #
         # That is to say, there is no guarantee that oldrev is a strict
         # subset of newrev (it would have required a --force, but that's
         # allowed).  So, we can't simply say rev-list $oldrev..$newrev.
         # Instead we find the common base of the two revs and list from
         # there.
         #
         # As above, we need to take into account the presence of X; if
         # another branch is already in the repository and points at some of
         # the revisions that we are about to output - we don't want them.
         # The solution is as before: git rev-parse output filtered.
        #
         # Finally, tags: 1 --- 2 --- O --- T --- 3 --- 4 --- N
         #
         # Tags pushed into the repository generate nice shortlog emails that
         # summarise the commits between them and the previous tag.  However,
         # those emails don't include the full commit messages that we output
         # for a branch update.  Therefore we still want to output revisions
         # that have been output on a tag email.
        #
         # Luckily, git rev-parse includes just the tool.  Instead of using
         # "--all" we use "--branches"; this has the added benefit that
         # "remotes/" will be ignored as well.

         # List all of the revisions that were removed by this update, in a
         # fast forward update, this list will be empty, because rev-list O
         # ^N is empty.  For a non fast forward, O ^N is the list of removed
         # revisions
         fast_forward=""
         rev=""
         for rev in $(git rev-list $newrev..$oldrev)
         do
                 revtype=$(git cat-file -t "$rev")
                 echo "  discards  $rev ($revtype)"
         done
         if [ -z "$rev" ]; then
                 fast_forward=1
         fi

         # List all the revisions from baserev to newrev in a kind of
         # "table-of-contents"; note this list can include revisions that
         # have already had notification emails and is present to show the
         # full detail of the change from rolling back the old revision to
         # the base revision and then forward to the new revision
         for rev in $(git rev-list $oldrev..$newrev)
         do
                 revtype=$(git cat-file -t "$rev")
                 echo "       via  $rev ($revtype)"
         done

         if [ "$fast_forward" ]; then
                 echo "      from  $oldrev ($oldrev_type)"
         else
                 #  1. Existing revisions were removed.  In this case newrev
                 #     is a subset of oldrev - this is the reverse of a
                 #     fast-forward, a rewind
                 #  2. New revisions were added on top of an old revision,
                 #     this is a rewind and addition.

                 # (1) certainly happened, (2) possibly.  When (2) hasn't
                 # happened, we set a flag to indicate that no log printout
                 # is required.

                 echo ""

                 # Find the common ancestor of the old and new revisions and
                 # compare it with newrev
                 baserev=$(git merge-base $oldrev $newrev)
                 rewind_only=""
                 if [ "$baserev" = "$newrev" ]; then
                         echo "This update discarded existing revisions and left the branch pointing at"
                         echo "a previous point in the repository history."
                         echo ""
                         echo " * -- * -- N ($newrev)"
                         echo "            \\"
                         echo "             O -- O -- O ($oldrev)"
                         echo ""
                         echo "The removed revisions are not necessarilly gone - if another reference"
                         echo "still refers to them they will stay in the repository."
                         rewind_only=1
                 else
                         echo "This update added new revisions after undoing existing revisions.  That is"
                         echo "to say, the old revision is not a strict subset of the new revision.  This"
                         echo "situation occurs when you --force push a change and generate a repository"
                         echo "containing something like this:"
                         echo ""
                         echo " * -- * -- B -- O -- O -- O ($oldrev)"
                         echo "            \\"
                         echo "             N -- N -- N ($newrev)"
                         echo ""
                         echo "When this happens we assume that you've already had alert emails for all"
                         echo "of the O revisions, and so we here report only the revisions in the N"
                         echo "branch from the common base, B."
                 fi
         fi

         echo ""
         if [ -z "$rewind_only" ]; then
                 echo "Those revisions listed above that are new to this repository have"
                 echo "not appeared on any other notification email; so we list those"
                 echo "revisions in full, below."

                 echo ""
                 echo $LOGBEGIN
                 show_new_revisions

                 # XXX: Need a way of detecting whether git rev-list actually
                 # outputted anything, so that we can issue a "no new
                 # revisions added by this update" message

                 echo $LOGEND
         else
                 echo "No new revisions were added by this update."
         fi

         # The diffstat is shown from the old revision to the new revision.
         # This is to show the truth of what happened in this change.
         # There's no point showing the stat from the base to the new
         # revision because the base is effectively a random revision at this
         # point - the user will be interested in what this revision changed
         # - including the undoing of previous revisions in the case of
         # non-fast forward updates.
         echo ""
         echo "Summary of changes:"
         git diff-tree --stat --summary --find-copies-harder $oldrev..$newrev
 }

#
# Called for the deletion of a branch
#
 generate_delete_branch_email()
 {
         echo "       was  $oldrev"
         echo ""
         echo $LOGEND
         git show -s --pretty=oneline $oldrev
         echo $LOGEND
 }

# --------------- Annotated tags

#
# Called for the creation of an annotated tag
#
 generate_create_atag_email()
 {
         echo "        at  $newrev ($newrev_type)"

         generate_atag_email
 }

#
# Called for the update of an annotated tag (this is probably a rare event
# and may not even be allowed)
#
 generate_update_atag_email()
 {
         echo "        to  $newrev ($newrev_type)"
         echo "      from  $oldrev (which is now obsolete)"

         generate_atag_email
 }

#
# Called when an annotated tag is created or changed
#
 generate_atag_email()
 {
         # Use git for-each-ref to pull out the individual fields from the
         # tag
         eval $(git for-each-ref --shell --format='
         tagobject=%(*objectname)
         tagtype=%(*objecttype)
         tagger=%(taggername)
         tagged=%(taggerdate)' $refname
         )

         echo "   tagging  $tagobject ($tagtype)"
         case "$tagtype" in
         commit)

                 # If the tagged object is a commit, then we assume this is a
                 # release, and so we calculate which tag this tag is
                 # replacing
                 prevtag=$(git describe --abbrev=0 $newrev^ 2>/dev/null)

                 if [ -n "$prevtag" ]; then
                         echo "  replaces  $prevtag"
                 fi
                ;;
         *)
                 echo "    length  $(git cat-file -s $tagobject) bytes"
                 ;;
         esac
         echo " tagged by  $tagger"
         echo "        on  $tagged"

         echo ""
         echo $LOGBEGIN

         # Show the content of the tag message; this might contain a change
         # log or release notes so is worth displaying.
         git cat-file tag $newrev | sed -e '1,/^$/d'

         echo ""
         case "$tagtype" in
         commit)
                 # Only commit tags make sense to have rev-list operations
                 # performed on them
                 if [ -n "$prevtag" ]; then
                         # Show changes since the previous release
                         git rev-list --pretty=short "$prevtag..$newrev" | git shortlog
                 else
                         # No previous tag, show all the changes since time
                         # began
                         git rev-list --pretty=short $newrev | git shortlog
                 fi
                ;;
         *)
                 # XXX: Is there anything useful we can do for non-commit
                 # objects?
                 ;;
         esac

         echo $LOGEND
 }

 #
 # Called for the deletion of an annotated tag
 #
 generate_delete_atag_email()
 {
         echo "       was  $oldrev"
         echo ""
         echo $LOGEND
         git show -s --pretty=oneline $oldrev
         echo $LOGEND
 }

# --------------- General references

#
# Called when any other type of reference is created (most likely a
# non-annotated tag)
#
 generate_create_general_email()
 {
         echo "        at  $newrev ($newrev_type)"

         generate_general_email
 }

#
# Called when any other type of reference is updated (most likely a
# non-annotated tag)
#
 generate_update_general_email()
 {
         echo "        to  $newrev ($newrev_type)"
         echo "      from  $oldrev"

         generate_general_email
 }

#
# Called for creation or update of any other type of reference
#
 generate_general_email()
 {
         # Unannotated tags are more about marking a point than releasing a
         # version; therefore we don't do the shortlog summary that we do for
         # annotated tags above - we simply show that the point has been
         # marked, and print the log message for the marked point for
         # reference purposes
         #
         # Note this section also catches any other reference type (although
         # there aren't any) and deals with them in the same way.

         echo ""
         if [ "$newrev_type" = "commit" ]; then
                 echo $LOGBEGIN
                 git show --no-color --root -s --pretty=medium $newrev
                 echo $LOGEND
         else
                 # What can we do here?  The tag marks an object that is not
                 # a commit, so there is no log for us to display.  It's
                 # probably not wise to output git cat-file as it could be a
                 # binary blob.  We'll just say how big it is
                 echo "$newrev is a $newrev_type, and is $(git cat-file -s $newrev) bytes long."
         fi
 }

#
# Called for the deletion of any other type of reference
#
 generate_delete_general_email()
 {
         echo "       was  $oldrev"
         echo ""
         echo $LOGEND
         git show -s --pretty=oneline $oldrev
         echo $LOGEND
 }


# --------------- Miscellaneous utilities

#
# Show new revisions as the user would like to see them in the email.
#
 show_new_revisions()
 {
         # This shows all log entries that are not already covered by
         # another ref - i.e. commits that are now accessible from this
         # ref that were previously not accessible
         # (see generate_update_branch_email for the explanation of this
         # command)

         # Revision range passed to rev-list differs for new vs. updated
         # branches.
         if [ "$change_type" = create ]
         then
                 # Show all revisions exclusive to this (new) branch.
                 revspec=$newrev
         else
                 # Branch update; show revisions not part of $oldrev.
                 revspec=$oldrev..$newrev
         fi

         other_branches=$(git for-each-ref --format='%(refname)' refs/heads/ |
             grep -F -v $refname)
         git rev-parse --not $other_branches |
         if [ -z "$custom_showrev" ]
         then
                 git rev-list --pretty --stdin $revspec
         else
                 git rev-list --stdin $revspec |
                 while read onerev
                 do
                         eval $(printf "$custom_showrev" $onerev)
                 done
         fi
 }


 send_mail()
 {
         if [ -n "$envelopesender" ]; then
                 /usr/sbin/sendmail -t -f "$envelopesender"
         else
                 /usr/sbin/sendmail -t
         fi
 }

# ---------------------------- main()

# --- Constants
 LOGBEGIN="- Log -----------------------------------------------------------------"
 LOGEND="-----------------------------------------------------------------------"

 # --- Config
 # Set GIT_DIR either from the working directory, or from the environment
 # variable.
 GIT_DIR=$(git rev-parse --git-dir 2>/dev/null)
 if [ -z "$GIT_DIR" ]; then
         echo >&2 "fatal: post-receive: GIT_DIR not set"
         exit 1
 fi

 projectdesc=$(sed -ne '1p' "$GIT_DIR/description")
 # Check if the description is unchanged from it's default, and shorten it to
 # a more manageable length if it is
 if expr "$projectdesc" : "Unnamed repository.*$" >/dev/null
 then
         projectdesc="UNNAMED PROJECT"
 fi

 recipients=$(git config hooks.mailinglist)
 announcerecipients=$(git config hooks.announcelist)
 envelopesender=$(git config hooks.envelopesender)
 emailprefix=$(git config hooks.emailprefix || echo '[SCM] ')
custom_showrev=$(git config hooks.showrev)

# --- Main loop
# Allow dual mode: run from the command line just like the update hook, or
# if no arguments are given then run as a hook script
 if [ -n "$1" -a -n "$2" -a -n "$3" ]; then
         # Output to the terminal in command line mode - if someone wanted to
         # resend an email; they could redirect the output to sendmail
         # themselves
         PAGER= generate_email $2 $3 $1
 else
         while read oldrev newrev refname
         do
                 generate_email $oldrev $newrev $refname | send_mail
         done
 fi

